U.S. patent number 6,768,238 [Application Number 10/285,392] was granted by the patent office on 2004-07-27 for rotor for a permanent magnet synchronous machine.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Axel Knauff, Rolf Vollmer.
United States Patent |
6,768,238 |
Knauff , et al. |
July 27, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Rotor for a permanent magnet synchronous machine
Abstract
A rotor for permanent magnet synchronous machines with a
reduction in the stray flux transmitted through the rotor shaft
includes substantially ring-shaped punched sheet metal plates with
a central opening for receiving the rotor shaft, and a plurality of
recesses arranged in the circumferential direction, wherein at
least two permanent magnets can be inserted in each of the
recesses. A corresponding intermediate sheet metal segment is
arranged or can be arranged in each of the recesses between the
permanent magnets. At least one of the recesses is shaped so as to
form an air gap between the surface of the intermediate sheet metal
segment that is oriented radially inwardly towards the center and
an edge of the recess that is oriented radially outwardly from the
center, when the permanent magnets are inserted radially towards
the outside. The air gap aids in attenuating the stray flux.
Inventors: |
Knauff; Axel (Munnerstadt,
DE), Vollmer; Rolf (Gersfeld, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Muchen, DE)
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Family
ID: |
7704339 |
Appl.
No.: |
10/285,392 |
Filed: |
October 31, 2002 |
Foreign Application Priority Data
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Oct 31, 2001 [DE] |
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101 53 750 |
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Current U.S.
Class: |
310/156.56;
310/156.53; 310/156.55; 310/156.57 |
Current CPC
Class: |
H02K
1/2773 (20130101) |
Current International
Class: |
H02K
1/27 (20060101); H02K 021/12 () |
Field of
Search: |
;310/156.55,156.56,156.57,156.58,156.59,156.6,156.61,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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135 955 |
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Jun 1979 |
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DE |
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197 23 302 |
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Dec 1998 |
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DE |
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0 803 962 |
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Oct 1997 |
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EP |
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0 872 944 |
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Oct 1998 |
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EP |
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2000156946 |
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Jun 2000 |
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JP |
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Primary Examiner: Mullins; Burton S.
Assistant Examiner: Comas; Yahveh
Attorney, Agent or Firm: Feiereisen; Henry M.
Claims
What is claimed is:
1. A punched sheet metal unit for electrical machines comprising a
substantially ring-shaped punched sheet metal plate having a
central opening adapted to receive a shaft; a plurality of recesses
formed in the sheet metal plate and arranged in a circumferential
direction of the sheet metal plate, each of said recesses adapted
to receive at least two permanent magnets, at least one of the
recesses being open at a peripheral edge of the sheet metal plate;
an intermediate sheet metal segment arranged between the at least
two permanent magnets, said intermediate sheet metal segment having
a peripheral edge and an inward edge facing the opening; a
plurality of separation sheet metal segments, which separate the
recesses from each other and are formed as a single piece with the
punched sheet metal plate, at least one of the separation sheet
metal segments has at least one tangentially arranged nose formed
proximate to the peripheral edge of the sheet metal plate, said
nose adapted to secure at least one of the permanent magnets
disposed in the at least one recess; and at least one holding
element received in a corresponding recess and adapted to hold the
at least two permanent magnets in the recess in a predetermined
position, wherein an air gap is formed between the inward edge of
the intermediate sheet metal segment and an edge of the recess
proximate to the opening when the at least two permanent magnets
are inserted so as to contact the respective recesses, and wherein
a first mounting recess is provided on the inward edge of the
intermediate sheet metal segment and a first second mounting recess
is provided on the edge of the recess proximate to the opening,
said first and second mounting recesses adapted for engagement with
the holding element.
2. The punched sheet metal unit of claim 1, wherein the at least
two permanent magnets includes surfaces facing the opening which
abut the air gap in at least one of the recesses.
3. The punched sheet metal unit of claim 1, wherein the
intermediate sheet metal segments are connected to the punched
sheet metal plate in a peripheral region of the punched sheet metal
plate.
4. The punched sheet metal unit of claim 3, wherein the
intermediate sheet metal segments are formed as one piece with the
punched sheet metal plate.
5. The punched sheet metal unit of claim 1, further comprising a
plurality of separation sheet metal segments, which separate the
recesses from each other and are formed as a single piece with the
punched sheet metal plate.
6. The punched sheet metal unit of claim 5, wherein the separation
sheet metal segments are connected with adjacent intermediate sheet
metal segments in a peripheral region of the punched sheet metal
plate.
7. The punched sheet metal unit of claim 5, wherein at least one of
the recesses is open at a peripheral edge of the sheet metal plate,
and wherein at least one of the separation sheet metal segments has
at least one tangentially arranged nose formed proximate to the
peripheral edge of the sheet metal plate, said nose adapted to
secure at least one of the permanent magnets disposed in the at
least one recess.
8. The punched sheet metal unit of claim 7, wherein the
intermediate sheet metal segments include on their inward edges
tangentially formed noses adapted to secure the permanent
magnets.
9. The punched sheet metal unit of claim 1, wherein the holding
element is made of a non-magnetic material.
10. The punched sheet metal unit of claim 9, wherein the
non-magnetic material is selected from the group consisting of
non-magnetic metals and plastics.
11. A punched sheet metal module having a plurality of connected
punched sheet metal units sequentially arranged in an axial
direction, the punched sheet metal units comprising: a
substantially ring-shaped punched sheet metal plate having a
central opening adapted to receive a shaft, a plurality of recesses
formed in the sheet metal plate and arranged in a circumferential
direction of the sheet metal plate, each of said recesses adapted
to receive at least two permanent magnets, an intermediate sheet
metal segment arranged between the at least two permanent magnets,
said intermediate sheet metal segment having a peripheral edge and
an inward edge facing the opening, wherein an air gap is formed
between the inward edge of the intermediate sheet metal segment and
an edge of the recess proximate to the opening when the at least
two permanent magnets are inserted so as to contact the respective
recesses, a separation sheet metal segment located between two of
the plurality of recesses and connected to the ring-shaped punched
sheet metal plate without a gap, wherein the intermediate sheet
metal segments having the gap and the separation sheet metal
segments without the gap are arranged periodically in an axial
direction of the punched sheet metal module.
12. The punched sheet metal module of claim 11, wherein the punched
sheet metal units are connected by at least one of impregnating and
gluing.
13. The punched sheet metal module of claim 11, and further
comprising substantially ring-shaped second punched sheet metal
plates with a central opening adapted to receive the shaft, and a
plurality of circumferentially arranged openings formed in the
second punched sheet metal plates and adapted to receive the at
least two permanent magnets, wherein the openings are aligned with
the recesses in the punched sheet metal units and the second
punched sheet metal plates are interposed between the sequentially
arranged punched sheet metal units.
14. The punched sheet metal module of claim 13, wherein the
predetermined number defines a periodic arrangement of the punched
sheet metal units and the second punched sheet metal plates.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application
Serial No. 101 53 750.6, filed Oct. 31, 2001, pursuant to 35 U.S.C.
119(a)-(d), the disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
The present invention relates to a rotor for an electric machine,
in particular a permanent magnet (PM) synchronous machine. More
particularly, the present invention relates to a punched sheet
metal unit for electrical machines with a substantially ring-shaped
punched metal plate, which has its center an opening for receiving
a shaft, and a plurality of recesses arranged along the periphery
of the metal plate, wherein one or more corresponding permanent
magnets can be inserted in the recesses.
The permanent magnets in a rotor of asynchronous machines excited
with permanent magnets are embedded radially in the rotor iron. The
permanent magnets can be arranged in a flux concentration
arrangement and magnetized alternatingly with different tangential
magnetization directions. A rotor of this type is described in EP 0
803 962 A1. The punched sheet metal packet of the rotor described
therein has an opening for receiving a holding element in the form
of a hollow cylinder. This holding element secures the permanent
magnets in the gaps of the sheet metal packet and should be made of
a non-magnetic material to avoid stray flux. The sheet metal packet
is held with screws between two coupling flanges to ensure its
stability. The bolts and/or screws extend through both coupling
flanges as well as through the sheet metal packet.
Rotors with permanent magnets implemented in a flux-concentrating
design have a fundamental problem in that stray flux .PHI..sub.s
can propagate through the shaft. The stray flux .PHI..sub.s can be
reduced by employing non-magnetic materials, air gaps or easily
saturable, thin soft-magnetic junction elements between the
permanent magnet and the shaft. However, such arrangements
disadvantageously either use expensive materials and have a complex
design, or still exhibit a residual, potentially significant stray
flux.
It would therefore be desirable and advantageous to provide an
improved rotor for a permanent magnet synchronous machine to
obviate prior art shortcomings and to minimize the stray flux
transmitted through the shaft while retaining a simple design of
the sheet metal packet.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a punched sheet metal
unit for electrical machines with a substantially ring-shaped
punched metal plate has in its center an opening for receiving a
shaft, and a plurality of recesses arranged in the circumferential
direction, wherein at least two permanent magnets can be inserted
in each of the recesses. A corresponding intermediate sheet metal
segment is arranged or can be arranged in each of the recesses
between the permanent magnets. At least one of the recesses is
shaped so as to form an air gap between the surface of the
intermediate sheet metal segment that is oriented radially inwardly
towards the center and an edge of the recess that is oriented
radially outwardly from the center, when the permanent magnets are
inserted radially towards the outside.
According to another aspect of the invention, a punched sheet metal
module includes a plurality of connected punched sheet metal units
sequentially arranged in an axial direction, with the punched sheet
metal units including a substantially ring-shaped punched metal
plate having a central opening adapted to receive a shaft, a
plurality of recesses formed in the metal plate and arranged in a
circumferential direction of the metal plate, each of said recesses
adapted to receive at least two permanent magnets, and an
intermediate sheet metal segment arranged between the at least two
permanent magnets. The intermediate sheet metal segment has a
peripheral edge and an inward edge facing the opening, wherein an
air gap is formed between the inward edge of the intermediate sheet
metal segment and an edge of the recess proximate to the opening
when the at least two permanent magnets are inserted in such a way
as to contact the respective recesses.
Embodiments of the invention may include one or more of the
following features. The air gap in at least one of the recesses can
abut surfaces of the at least two permanent magnets that are
oriented towards the opening. The intermediate sheet metal segments
can be connected in a peripheral region of the punched sheet metal
and also formed as one piece with the punched sheet metal.
Additionally employed separation sheet metal segments which can be
formed as one piece with the punched sheet metal can be provided to
separate the recesses from each other. The separation sheet metal
segments can be connected with adjacent intermediate sheet metal
segments in a peripheral region of the punched metal plate.
Advantageously, at least one of the recesses can be open at a
peripheral edge of the metal plate and at least one of the
separation sheet metal segments can have at least one tangentially
arranged nose formed proximate to the peripheral edge of the metal
plate, wherein the nose can hold at least one of the permanent
magnets disposed in a recess. The permanent magnets can also be
held in place by providing the intermediate sheet metal segments on
their inward edges with tangentially formed noses. Alternatively,
to prevent the intermediate sheet metal segments and/or the
permanent magnets from being ejected by the centrifugal force, at
least one holding element can be disposed in a corresponding recess
and configured to hold the at least two permanent magnets in the
recess in a predetermined position. The holding element can be
secured by providing mounting recesses in the inward edge of the
intermediate sheet metal segment and in the edge of the recess
proximate to the opening, wherein the mounting recesses can engage
with the holding element. To minimize the stray flux, the holding
element can be made of a non-magnetic material, such as aluminum,
an aluminum alloy, brass, non-magnetic stainless steel and
plastics.
The punched sheet metal units of the punched sheet metal module can
be connected with each other by one or more bolts extending through
the punched sheet metal units, an/or by impregnating, potting
and/or gluing.
BRIEF DESCRIPTION OF THE DRAWING
Other features and advantages of the present invention will be more
readily apparent upon reading the following description of
currently preferred exemplified embodiments of the invention with
reference to the accompanying drawing, in which:
FIG. 1 is a top view of a punched sheet metal unit according to a
first embodiment of the present invention;
FIG. 1A is a top view of a punched sheet metal plate used to secure
the magnets;
FIG. 2 is a top view of a punched sheet metal unit according to a
second embodiment of the present invention;
FIG. 3 is a top view of a punched sheet metal unit according to a
third embodiment of the present invention; and
FIG. 4 is a perspective view of a sheet metal module with punched
sheet metal units according to the third embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Throughout all the Figures, same or corresponding elements are
generally indicated by same reference numerals.
Turning now to the drawing, and in particular to FIG. 1, there is
shown a top view of a punched sheet metal plate 10 according to a
first embodiment of the present invention. The punched sheet metal
plate 10 includes a center opening 12 adapted for insertion of a
rotor shaft. The ring-shaped punched sheet metal plate 10 also has
U-shaped punched out sections and/or recesses 13 arranged on a
circle. The legs 14 of the recesses 13 extend radially outwardly.
Punched-out tongues or intermediate sheet metal segments 15 are
formed between the legs 14 of each recess 13. Sheet metal segments
which will be referred to hereinafter as separation sheet metal
segments 16, are disposed between every other recess 13. The legs
14 of the recesses 13 do not extend to the outer peripheral edge of
the punched sheet metal plate 10, leaving a connecting web 17 at
the head of each leg, which connects an intermediate sheet metal
segment 15 with a separation sheet metal segment 16.
FIG. 1 also indicates the configuration of the permanent magnets 18
inserted in each leg of the U-shaped recesses 13. The North poles
of the permanent magnets disposed in the legs of the same recess 13
face each other. This produces a stray flux .PHI..sub.s extending
from the tip of the intermediate sheet metal segment 15 to the
interior section of the ring-shaped punched sheet metal plate 10.
The stray flux .PHI..sub.s is attenuated significantly since it has
to bridge the air gap .delta..sub.s between the tip of the
intermediate sheet metal segments 15 and the interior section of
the punched sheet metal plate 10. The useful flux .PHI..sub.N, on
the other hand, can optimally exit and reenter at the outer
circumference of the rotor in the radial direction, since both the
intermediate sheet metal segments 15 and the separation sheet metal
segments 16 are oriented in the radial direction.
FIG. 2 shows a second embodiment of the present invention, wherein
the recesses 23 are open in the radially outward direction. This
exemplary configuration shows the permanent magnets 18 as also
being mounted in the recesses 23.
Unlike in the first embodiment of FIG. 1, where the intermediate
sheet metal segments 15 were connected tangentially with a
corresponding adjacent separation sheet metal segment 16 by a
connecting web 17, the intermediate sheet metal segments 25 are in
the embodiment depicted in FIG. 2 not an integral part of the
punched sheet metal plate 20. A holding element 29 secures each
installed intermediate sheet metal segment 25 against the
centrifugal force. For example, the holding element 29 can engage
with a punched-out section disposed in the end face of the
intermediate sheet metal segment 25 facing the center and with a
punched-out section 21 disposed in the metal plate 20 on the
section of the recesses 23 proximate the opening 12. The engagement
between the ends of the holding element 29, which can have a
circular cross-section, and the circular recesses on the
intermediate sheet metal segment 25 and the punched sheet metal
plate 20 produces a force-transmitting connection.
The permanent magnets 18 are secured against the centrifugal force
by tangential noses 28 arranged on both sides of each separation
sheet metal segment 26 proximate to the outer periphery of the
punched sheet metal plate 20. The permanent magnets 18 can also be
secured in the centripetal direction by forming the holding element
29 with legs 27 which secure the permanent magnets 18 radially in
each recess 23.
The holding element 29 assists in the assembly of a rotor by
holding the permanent magnets 18 in place with respect to the sheet
metal packets when the sheet metal packets are stacked to a module,
for example, the modules 41 and 42 depicted in FIG. 4. The holding
elements 29 have the additional function of stabilizing the
intermediate sheet metal segments of rotors operating at high
rotation speeds.
FIG. 3 shows schematically in a top view a third embodiment of the
present invention. Unlike the second embodiment, the third
embodiment does not have recesses for the holding elements 29 in
the punched sheet metal plate 30 are not required.
However, as in the second embodiment, the permanent magnets 18 in
the third embodiment are secured against the centrifugal force by
noses 28 formed on the separation sheet metal segments 26. The
intermediate sheet metal segments 35 which are form-fittingly
arranged in a recess 23 between the permanent magnets 18, also have
tangentially oriented noses 31 on the side facing the center, which
support the noses 31 on the permanent magnets 18 against the
centrifugal force. This embodiment also includes the air gap
.delta..sub.s of the invention located between the intermediate
sheet metal segment 35 and the punched sheet metal plate 30,
whereby the punched sheet metal plate 30 has a comparatively simple
punched-out shape.
FIG. 4 is a schematic three-dimensional view of two exemplary sheet
metal modules 41 and 42, each of which can be made of a stack of
axially superpositioned punched sheet metal plates, such as the
illustrated plates 30 according to the third embodiment, as well as
installed permanent magnets 18 and intermediate sheet metal
segments 35. However, any of the embodiments described above or a
combination of plates 10, 20, 30 can be used. Such sheet metal
modules can be applied with greater flexibility than rotor-specific
sheet metal packets and are easier to assemble.
Referring back to FIGS. 1-3 and also to FIG. 1A, in yet another
embodiment the arrangement of the sheet metal units 10 can be
modified so that the intermediate sheet metal segments 15 and the
separation sheet metal segments 16 are formed identically, for
example periodically, on every x.sup.th metal sheet, such as every
5.sup.th sheet. As shown in FIG. 1A, in this case a sheet metal
plate 10' includes openings for the magnets 18 which are closed
towards the center opening 12. Each of the at least two magnets 18
is separated by a separation sheet metal segment 16'. The small
number of sheet metal plates 10' compared to the number of sheet
metal units 10 will still be capable of supporting the permanent
magnets in the centripetal direction, while the comparatively
larger number of sheet metal units 10 with the air gap
.delta..sub.s still keeps the stray flux .PHI..sub.s small.
A plurality of sheet metal modules can be stacked along the axial
direction, wherein each sheet metal packet module can
advantageously be rotated relative to an adjacent sheet metal
packet module by a predetermined angle, as schematically indicated
in FIG. 4. This produces over the axial length of the successive
sheet metal modules a pole skew which can in turn reduce slot
latching and an associated slot latching torque.
The aforedescribed modules 41, 42 can also be assembled, for
example, by combining the punched sheet metal plates 10 depicted in
FIG. 1 with the punched sheet metal plates 30 depicted in FIG. 3.
This has the advantage that the permanent magnets 18 are secured
against the centrifugal force without requiring the presence of
noses 28 in the punched metal sheets 30 of FIG. 3.
While the invention has been illustrated and described in
connection with currently preferred embodiments shown and described
in detail it is not intended to be limited to the details shown
since various modifications and structural changes may be made
without departing in any way from the spirit of the present
invention. The embodiments were chosen and described in order to
best explain the principles of the invention and practical
application to thereby enable a person skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated.
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims and their
equivalents.
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